U.S. patent number 4,237,077 [Application Number 05/937,896] was granted by the patent office on 1980-12-02 for automatic choke system.
This patent grant is currently assigned to Texas Instruments Incorporated. Invention is credited to Peter G. Berg.
United States Patent |
4,237,077 |
Berg |
December 2, 1980 |
Automatic choke system
Abstract
An automatic choke system of modular construction has
self-regulating heaters arranged to heat a thermostatic spring to
adjust a choke valve during start-up of an automotive engine. Heat
storing and transferring means are located between the heaters and
spring to provide heat-transfer paths of different lengths between
the respective heaters and the spring for providing the
thermostatic spring with non-linear heat up to improve the
smoothness of initial engine operation while also minimizing the
period of fuel-enriched operation during start-up. The same heat
storing and transferring means is also provided with a large heat
storing capacity for continuing to transfer heat to the spring
after termination of engine operation to prevent any substantial
fuel enrichment by the choke system if the engine should be
restarted before selected portions of the engine cool below
selected fuel vaporizing temperatures.
Inventors: |
Berg; Peter G. (Norton,
MA) |
Assignee: |
Texas Instruments Incorporated
(Dallas, TX)
|
Family
ID: |
25470540 |
Appl.
No.: |
05/937,896 |
Filed: |
August 29, 1978 |
Current U.S.
Class: |
261/39.6;
123/588; 219/206; 219/505; 236/101C; 337/107; 338/22R |
Current CPC
Class: |
F02M
1/12 (20130101); F02D 2200/0606 (20130101) |
Current International
Class: |
F02M
1/00 (20060101); F02M 1/12 (20060101); F02M
001/12 () |
Field of
Search: |
;261/39E ;123/119F
;236/11C ;337/104,107 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Oldsmobile Service Manual, 1978 Chassis, pp. 6C1-34 and
6C1-35..
|
Primary Examiner: Miles; Tim R.
Attorney, Agent or Firm: McAndrews; James P. Haug; John A.
Sharp; Melvin
Claims
I claim:
1. In combination with an internal combustion engine having
air-fuel portions which warm above a selected temperature during
engine operation and assure full vaporization of the fuel in an
air-fuel mixture being furnished to the engine and which tend to
cool below that temperature within a delay period after termination
of engine operation, an electrical power source, and a carburetor
having an air-fuel induction passage furnishing an air-fuel mixture
to the engine and having an unbalance-mounted, air-movable choke
valve mounted for variable movement across the passage to control
air flow through the passage, a choke control system comprising
thermostatic spring means urging the choke valve toward a closed
position in the passage with a force increasing as a function of
decreases in the temperature of the spring means from a
predetermined level to provide a fuel enriched air-fuel mixture to
the engine on a first initiation of engine operation, electrical
heater means operable from said power source during operation of
the engine, and heat storing and transferring means disposed
between the heater means and spring means for receiving and storing
heat from the heater means and for transferring such heat to the
spring means to reduce the choke valve closing force of the spring
means and permit sufficient opening of the valve by the flow of air
through the passage against the valve to substantially eliminate
such fuel enrichment after said engine portions have become heated
to said selected temperature, said heat storing and transferring
means having sufficient heat storage capacity to continue to
transfer heat to the spring means for a time after termination of
engine operation so that for a major part of said delay period the
spring means are maintained at a temperature preventing any
substantial fuel enrichment of the air-fuel mixture on a restarting
of the engine, said heater means comprising a first heater device
operable on initiation of engine operation, a second heater device,
and thermally responsive switch means actuable above a
predetermined ambient temperature to operate the second heater
device, said heat storing and transferring means having one side
lying along said spring means to transfer heat to the spring means,
having a first surface portion with a selected spacing from said
one side having said first heater device secured in heat-transfer
relation thereto defining a first heat-transfer path of a selected
length between the first heater device and the spring means for
initiating heat transfer to the spring means with a selected delay
after the initiation of engine operation when ambient temperature
is below said predetermined ambient temperature, and having a
second surface portion with a relatively much smaller spacing from
said one side having said second heater device secured in heat
transfer relation thereto defining a second, relatively much
shorter heat-transfer path between the second heater device and the
spring means for initiating heat-transfer to the spring means
promptly after the initiation of engine operation when ambient
temperature is above said predetermined ambient temperature.
2. A choke control system as set forth in claim 1 wherein said
heat-transfer means defines a third heat-transfer path between the
first heater device and the thermally responsive switch means for
heating the switch means to the actuation temperature thereof, said
third heat-transfer path being adapted to transfer sufficient heat
to the switch means when the ambient temperature is below said
predetermined ambient temperature for actuating the switch means to
initiate operation of the second heater device after the initiation
of heat-transfer to the spring means has begun and before the
spring means have been heated to the temperature at which said fuel
enrichment of the air-fuel mixture has been substantially
eliminated.
3. In combination with an internal combustion engine having
air-fuel portions which warm above a selected temperature during
engine operation and assure full vaporization of the fuel in an
air-fuel mixture being furnished to the engine and which tend to
cool below that temperature within a delay period after termination
of engine operation, an electrical power source, and a carburetor
having an air-fuel induction passage furnishing an air-fuel mixture
to the engine and having an unbalance-mounted, air-movable choke
valve mounted for variable movement across the passage to control
air flow through the passage, a choke control system comprising
thermostatic spring means urging the choke valve toward a closed
position in the passage with a force increasing as a function of
decreases in the temperature of the spring means from a
predetermined level to provide a fuel enriched air-fuel mixture to
the engine on a first initiation of engine operation, electrical
heater means operable from said power source during operation of
the engine, said heater means comprising a first heater device
operable on initiation of engine operation, a second heater device,
and thermally responsive switch means actuable above a
predetermined ambient temperature to operate the second heater
device, and heat-transfer means disposed between the heater means
and spring means for receiving and storing heat from the heater
means and for transferring such heat to the spring means to reduce
the choke valve closing force of the spring means and permit
sufficient opening of the valve by the flow of air through the
passage against the valve to substantially eliminate such fuel
enrichment after said engine portions have become heated to said
selected temperature, said heat-transfer means defining a first
heat-transfer path of a selected length between the first heater
device and the spring means for initiating heat transfer to the
spring means with a selected delay after the initiation of engine
operation when ambient temperature is below said predetermined
ambient temperature, said heat-transfer means defining a second,
relatively much shorter heat-transfer path between the second
heater device and the spring means for initiating heat-transfer to
the spring means promptly after the initiation of engine operation
when ambient temperature is above said predetermined ambient
temperature, said heat-transfer means having sufficient heat
storage capacity to continue to transfer heat to the spring means
for a time after termination of engine operation so that for a
major part of said delay period the spring means are maintained at
a temperature preventing any substantial fuel enrichment of the
air-fuel mixture on a restarting of the engine, said choke control
system having a modular construction wherein said heat storing and
transferring means includes a first relatively thin heat sink plate
mounting said second heater device in closely spaced heat-transfer
relation to the thermostatic spring means, and a second relatively
much thicker heat-sink plate secured in heat-transfer relation to
the first plate, the second plate mounting the first heater device
in relatively greater spaced relation to the thermostatic spring
means.
4. A choke control system as set forth in claim 3 wherein the
spring means comprise a spiral thermostat coil, the first heat sink
plate mounts the coil at one side of the first plate, the second
heater device comprises a self-regulating electrical resistance
heater element of a ceramic material of positive temperature
coefficient of resistivity secured in heat-transfer relation to the
first plate at the center of the opposite side of the first plate,
the second heat sink plate has one side secured in heat transfer
relation to said opposite side of the first plate, has a central
opening fitted around said second heater device, and has a tang
extending from the opposite side of the second plate over said
opening, and said first heater device comprises a self-regulating
electrical resistance element of a ceramic material of positive
temperature coefficient of resistivity secured to said tang in heat
transfer relation to the second plate.
5. A choke control system as set forth in claim 4 having selected
thermal insulating means secured between portions of said first and
second heat-sink plates for limiting the rate of heat-transfer
between said plates.
6. A choke control system as set forth in claim 4 wherein said heat
sink plates respectively connect one side of the heater elements to
electrical ground, a conductor is connected to the other side of
the heater element on the first plate and extends through the
opening in the second plate in electrically insulated relation to
the second plate, and housing means of electrical insulating
material mount the thermally responsive switch means connected to
the power source and mount additional terminal means connected to
the power source, said housing means being secured to said opposite
side of the second heat sink plate connecting the switch means to
said conductor and connecting the additional terminal means to the
other side of the heater element on the second heat sink plate.
7. A choke control system as set forth in claim 6 having thermal
insulation means surrounding the heat sink plates, heater elements
and thermostatic coil spring to retain heat therein so that the
heat-transfer means continues to transfer heat to the spring for a
sufficient time after termination of engine operation so that
substantially throughout said full delay period the spring is
maintained at a temperature preventing any substantial fuel
enrichment of the air-fuel mixture on such restarting of the
engine.
8. A choke control for use with a carburetor having an air-fuel
induction passage for furnishing an air-fuel mixture to an engine
and having an unbalance mounted, air-movable choke valve mounted
for variable movement across the passage to control air-flow
through the passage comprising thermostatic spring means urging the
choke valve toward a closed position in the passage with a force
increasing as a function of decreases in the temperature of the
spring means from a predetermined level for providing a fuel
enriched air-fuel mixture to the engine on initiation of engine
operation, a first electrical heater operable on initiation of
engine operation, a second electrical heater, thermally responsive
switch means actuable above a predetermined ambient temperature for
energizing the second heater, and heat storing and transferring
means disposed between the heaters and spring means for receiving
heat from the heaters and for transferring such heat to the spring
means to reduce the choke valve closing force of the spring means
and permit opening of the choke valve by the flow of air through
the passage against the valve to substantially eliminate such fuel
enrichment, said heat storing and transferring means having one
side lying along said spring means to transfer heat to the spring
means, having a first surface portion with a selected spacing from
said one side having said first heater secured in heat-transfer
relation thereto defining a first heat-transfer path of selected
length between the first heater and the spring means for initiating
heater transfer to the spring means with a selected delay after the
initiation of engine operation when ambient temperature is below
said predetermined ambient temperature, and having a second surface
portion with a relatively much smaller spacing from said one side
having said second heater secured in heat-transfer relation thereto
defining a second, relatively much shorter heat-transfer path
between the second heater and the spring means for initiating heat
transfer to the spring means promptly after the initiation of
engine operation when ambient temperature is above said
predetermined ambient temperature.
9. A choke control as set forth in claim 8 wherein said
heat-transfer means defines a third heat-transfer path between the
first heater and the thermally responsive switch means for heating
the switch means to the actuation temperature thereof, said third
heat-transfer path being adapted to transfer sufficient heat to the
switch means when the ambient temperature is below said
predetermined ambient temperature for actuating the switch means to
initiate operation of the second heater device after the initiation
of heat-transfer to the spring means has begun and before the
spring means have been heated to the temperature at which said fuel
enrichment of the air-fuel mixture has been substantially
eliminated.
10. A choke control for use with a carburetor having an air-fuel
induction passage for furnishing an air-fuel mixture to an engine
and having an unbalance mounted, air-movable choke valve mounted
for variable movement across the passage to control air-flow
through the passage comprising thermostatic spring means urging the
choke valve toward a closed position in the passage with a force
increasing as a function of decreases in the temperature of the
spring means from a predetermined level for providing a fuel
enriched air-fuel mixture to the engine on initiation of engine
operation, a first electrical heater operable on initiation of
engine operation, a second electrical heater, thermally responsive
switch means actuable above a predetermined ambient temperature for
energizing the second heater, and heat-transfer means disposed
between the heaters and spring means for receiving heat from the
heaters and for transferring such heat to the spring means to
reduce the choke valve closing force of the spring means and permit
opening of the choke valve by the flow of air through the passage
against the valve to substantially eliminate such fuel enrichment,
said heat-transfer means defining a first heat-transfer path of
selected length between the first heater and the spring means for
initiating heat transfer to the spring means with a selected delay
after the initiation of engine operation when ambient temperature
is below said predetermined ambient temperature, said heat-transfer
means defining a second, relatively much shorter heat-transfer path
between the second heater and the spring means for initiating heat
transfer to the spring means promptly after the initiation of
engine operation when ambient temperature is above said
predetermined ambient temperature, said control having a modular
construction wherein said heat-transfer means include a first,
relatively thin heat sink plate mounting said second heater in
closely spaced heat-transfer relation to the thermostatic spring
means, and a second relatively much thicker heat-sink plate secured
in heat-transfer relation to the first plate, the second plate
mounting the first heater in relatively greater spaced relation to
the thermostatic spring means.
11. A choke control system as set forth in claim 10 wherein the
spring means comprise a spiral thermostat coil, the first heat sink
plate mounts the coil at one side of the first plate, the second
heater comprises a self-regulating electrical resistance heater
element of a ceramic material of positive temperature coefficient
of resistivity secured in heat-transfer relation to the first plate
at the center of the opposite side of the first plate, the second
heat sink plate has one side secured in heat transfer relation to
said opposite side of the first plate, has a central opening fitted
around said second heater, and has a tang extending from the
opposite side of the second plate over said opening, and said first
heater comprises a self-regulating electrical resistance element of
a ceramic material of positive temperature coefficient of
resistivity secured to said tang in heat transfer relation to the
second plate.
12. A choke control system as set forth in claim 11 having selected
thermal insulating means secured between portions of said first and
second heat-sink plates for limiting the rate of heat-transfer
between said plates.
13. A choke control system as set forth in claim 11 wherein said
heat sink plates respectively connect one side of the heater
elements to electrical ground, a conductor is connected to the
other side of the heater element on the first plate and extends
through the opening in the second plate in electrically insulated
relation to the second plate, and housing means of electrical
insulating material mount the thermally responsive switch means to
be connectable to a power source and mount additional terminal
means to be connectable to the power source, said housing means
being secured to said opposite side of the second heat sink plate
connecting the switch means to said conductor and connecting the
additional terminal means to the other side of the heater element
on the second heat sink plate.
Description
Automatic choke systems conventionally include a spiral
thermostatic spring which urges an unbalance-mounted, air-movable
choke valve in the air-fuel induction passage of a carburetor
toward a closed position in the passage with a force which
increases as a function of decreases in the temperature of the
spring. When the spring applies a selected force, the valve
restricts air entry to the passage and furnishes a fuel enriched
air-fuel mixture to an engine so that the engine tends to run
smoothly during its start-up period even though the engine may be
too cold to fully vaporize the fuel being furnished to the engine.
A pair of self-regulating electrical resistance heaters transfer
heat to the spring for progressively reducing its choke valve
closing force and for permitting the valve to move to an open
position in the passage in response to the flow of air through the
passage against the valve. The first heater is energized when
engine operation is initiated and the second heater is energized
when a thermally responsive switch is actuated above a
predetermined ambient temperature. In such conventional choke
systems, the spring begins to receive heat from the first heater
promptly after the engine is started so that the choke valve
closing force is reduced to eliminate the fuel enrichment within a
selected period of time on a cold day when the engine has been
properly warmed up. If the engine is started when ambient
temperature is above the noted level, the spring promptly receives
heat from both heaters for more quickly reducing the choke valve
closing force of the spring.
In using such conventional systems, it is found that the initial
heating of the thermostatic spring tends to significantly reduce
the choke valve closing force of the spring. Accordingly, if the
engine is sharply accelerated shortly after engine start-up, the
flow of air against the choke valve could result in excessive
leaning of the air-fuel mixture and could cause rough operation or
even stalling of the engine. It would be desirable if an automatic
choke system could assure that the initially high level of fuel
enrichment provided on a cold day were maintained for a
sufficiently long period of time to assure smooth start-up
operation of the engine while still being adapted to reduce the
choke valve closing force of the spring to eliminate such fuel
enrichment within substantially the same total length of time as in
previously known choke systems.
In using conventional choke systems it has also been found that the
thermostatic spring tends to cool much more rapidly than the engine
when the heaters are deenergized at termination of the engine
operation. As a result, if the engine is restarted after the
thermostatic spring has cooled but while the engine is still warm,
the choke system tends to provide unnecessary fuel enrichment which
is wasteful of fuel, which produces escessive and unnecessary
exhaust emission of air pollutants, and which can even result in
flooding of the engine. Racing of the engine can also occur
particularly where fast idle cam means are also operated in
response to movement of the thermostatic spring. It would be
desirable if the choke system could prevent unnecessary fuel
enrichment on engine restarting and would be adapted to restore
fuel-enriching choke valve closing force to the spring only after
cool down of the engine.
It is an object of this invention to provide a novel and improved
automatic choke system for an automotive engine; to provide such a
system which assures that a properly fuel enriched air-fuel mixture
is furnished to the engine for a sufficient period of time after
engine start-up on a cold day to assure smooth operation of the
engine until the engine is warmed up; to provide such a system
which terminates any fuel enrichment in the mixture being furnished
to the engine promptly after warm-up of the engine is completed; to
provide such an improved choke system which prevents furnishing of
a fuel enriched air-fuel mixture to the engine on restarting of the
engine unless the engine has cooled sufficiently to require such
fuel enrichment; and to provide such an improved choke system
having a construction which is adapted to be readily modified to
match the choke valve operating times of the system to the warm-up
and cool-down characteristics of various automotive engines.
Briefly described, the novel and improved automatic choke system of
this invention comprises a pair of self-regulating electrical
resistance heaters of positive temperature coefficient of
resistivity arranged to heat a spiral thermostatic spring. The
first heater is adapted to be energized when operation of an
automotive engine is initiated and the system includes a thermally
responsive switch which is actuable above a predetermined ambient
temperature to energize the second heater.
Novel heat-transfer means are disposed between the heaters and the
spring for receiving and storing heat from the heaters and for
transferring that heat to the spring. Those novel heat-transfer
means define a first heat-transfer path of selected effective
length between the first heater and the spring and also define a
second, much shorter heat transfer path between the second heater
and the spring. Preferably for example, the first heater is mounted
on a relatively thick heat-sink plate and the second heater is
mounted on a relatively thin heat sink plate. The two heat sink
plates are then secured together and the thermostatic spring is
mounted at one side of the thin heat sink plate to form the desired
two different heat-transfer paths.
In that arrangement, when the first heater is energized on engine
start-up on a cold day, the actual transfer of heat to the
thermostatic spring begins only with a selected delay after the
engine starting. That is, the heat initially received from the
first heater by the heat-transfer means is transferred to the
spring only with a delay after engine starting as the heat is
conducted along the relatively long first heat-transfer path. As a
result, the initial choke valve closing force of the thermostatic
spring is maintained for a time after engine start-up to assure
proper fuel enrichment and smooth engine operation during the
start-up period. However, when the engine is started on a warm day,
heat from the second heater is promptly transferred to the
thermostatic spring for substantially immediately initiating
reduction of the choke valve closing force of the spring for
assuring prompt termination of fuel enrichment by the choke
system.
In the novel and improved choke system of this invention, the heat
transfer means are also proportioned to have a substantial heat
storing capacity and are arranged to be fully heated by the heaters
during operation of the automobile engine. Accordingly, the heat
transfer means are adapted to continue to transfer heat to the
thermostatic spring for a substantial period of time after
operation of the engine is terminated so that, for at least a major
part of the time before the engine cools down, the thermostatic
spring is maintained at a temperature which would prevent any
substantial fuel enrichment by the choke system if the engine
should be restarted within that time.
Other objects, advantages and details of the novel and improved
automatic choke system of this invention appear in the following
detailed description of preferred embodiments of the invention, the
detailed description referring to the drawings in which:
FIG. 1 is a partial perspective view of an automotive engine having
a carburetor mounted thereon and having the novel and improved
automotive choke control of the invention arranged to regulate
operation of the choke valve on the carburetor;
FIG. 2 is a section view along line 2--2 of FIG. 1;
FIG. 3 is a section view along line 3--3 of FIG. 2; and
FIGS. 4 and 5 are graphs illustrating characteristics of the choke
control system of this invention.
Referring to the drawings, 10 in FIGS. 1 and 2 indicates the novel
and improved automatic choke control for an automotive engine
provided by this invention. The control is shown mounted on a
carburetor 12 on a typical internal combustion automotive engine
14. The carburetor 12 is fully conventional and, as will be
understood, includes an air-fuel induction passage 16 which is open
at one end 16.1 to admit air to the passage and which is connected
at its opposite end to the intake manifold 14.1 of the engine in
conventional manner. In that arrangement, the carburetor is adapted
to furnish an air-fuel mixture to the engine through the passage,
and throttle means (not shown) are selectively movable in the
carburetor for regulating the volume of the air-fuel mixture
furnished to the engine.
As will be understood, air-fuel intake portions of the engine such
as the intake manifold 14.1 and the like become heated during
operation of the engine so that as the air-fuel mixture being
furnished to the engine passes over those engine portions the fuel
constituent of the mixture is assured of being fully vaporized.
However, those engine portions typically require up to about six
minutes to reach that full vaporizing temperature when operation of
the engine is initiated on a cold day when ambient temperature is
on the order of 0.degree. F. or below. On the other hand, those
air-fuel intake portions of the engine also typically remain at or
above that selected fuel vaporizing temperature for as much as
20-30 minutes or more after termination of engine operation even on
a fairly cold day.
Accordingly, the carburetor 12 has a conventional unbalance
mounted, air-movable choke valve 18 mounted in the air-fuel
induction passage 16 of the carburetor for variable movement across
the passage 16 to control air flow through the passage. A
conventional bell crank 18.1 is mounted in the choke mounting
housing 12.1 of the carburetor and linkage 18.2 connects the bell
crank to the choke valve 18 for rotating the choke valve in
response to rotation of the bell crank in conventional manner.
Typically for example, the choke valve 18 is adapted to be rotated
from a position which substantially closes the air-fuel induction
passage 16 and wherein the valve extends at an angle of a few
degrees to the axis of the passage to a position which
substantially opens the passage and wherein the valve extends
substantially parallel to the passage axis. In that arrangement the
choke valve is adapted to be disposed in a closed position in the
passage 16 when the engine is initially started up, whereby the
entry of air into the passage is restricted and the air-fuel
mixture furnished to the engine by the carburetor is enriched so
that even if the fuel constituent is not fully vaporized by the
noted air-fuel intake portions of the engine, the mixture is still
adapted to provide suitably smooth operation of the engine. On the
other hand, the choke valve is adapted to be moved to a fully open
position in the passage 16 so that the carburetor supplies a lean
air-fuel mixture to the engine after the noted air-fuel intake
portions of the engine have heated to the noted fuel vaporizing
temperature and when enrichment of the air-fuel mixture being
furnished to the engine is no longer required. In that way, the
choke valve is adapted to save fuel and to reduce the amount of
unburned hydrocarbons and other pollutants which are emitted to the
atmosphere in the engine exhaust.
In accordance with the invention, the choke control 10 includes a
conventional thermostatic bimetal spiral coil spring 20 which is
fixed at one end to a stud 20.1 and which has a tang 20.2 at its
opposite end which is connected to the bell crank 18.1 for
adjusting the choke valve 18. That is, the spring 20 is operably
connected to the choke valve for urging the choke valve toward a
closed position in the passage 16 with a force which increases as a
function of decreases in the temperature of the spring from a
predetermined temperature level. The spring is normally adapted to
dispose the choke valve in the closed position in the passage 16
but when heated to reduce the choke valve closing force of the
spring permits opening of the valve by the flow of air through the
passage 16 against the valve.
In accordance with this invention, the choke control 10 further
includes a housing 22 of phenolic material or other rigid
electrical insulating material having a first recess 22.1 formed in
one side of the housing and having a second recess 22.2 formed in
the opposite side of the housing. A thermally responsive electrical
switch 24, comprising a snap-acting electrically conductive bimetal
disc 24.1 and a spider spring 24.2 or the like, is disposed in the
housing recess 22.2 as shown in FIG. 2. A spring terminal 26 is
secured in the recess 22.1 by a rivet 26.1 which extends through an
aperture 22.3 in the housing into recess 22.2. A second spring
terminal 28 is secured in the recess 22.1 by a second rivet 28.1.
The second rivet extends through an aperture 22.4 in the housing
and further secures a plate terminal 30 to the housing over the
recess 22.2 and electrically connects that terminal 30 to the
spring terminal 28. An additional screw 32 preferably extends
through terminal 30 to further secure the terminal 30 and a
terminal insulator 32.1 to the housing. In that arrangement, the
terminal 30 is adapted to be connected to a battery or other
electrical power source on the automotive engine by closing of the
engine ignition switch or the like (not shown) whenever the engine
14 is in operation, thereby to direct electrical current to the
spring terminal 28 when the engine is being operated. The snap
acting disc 24.1 is normally spaced from the rivet 26.1 so that the
terminal 30 does not normally direct electrical current to the
spring terminal 26. However, the snap-acting disc 24.1 is adapted
to be actuated and to move to an inverted domed configuration from
that shown in FIG. 2 when the disc is heated above a predetermined
ambient temperature such as 70.degree. F. When that occurs, the
disc electrically engages the rivet 26.1 and electrically connects
that rivet to the terminal 30 through the disc 24.1 and the spider
spring 24.2 for directing electrical current to the spring terminal
26.
The choke control 10 additionally comprises first and second
electrical resistance heaters 34 and 36. The control also comprises
heat-transfer means including the metal heat-sink plates 38 and 40
which are disposed between the heaters and the thermostatic spring
20, which receive and store heat from the heaters, and which
transfer such heat to the spring 20. In accordance with this
invention, the heat-transfer means define a first heat-transfer
path of substantial length between the first heater 34 and the
spring 20 as is illustrated in FIG. 2 and also define a second,
much shorter heat-transfer path between the second heater 36 and
the spring 20.
In a preferred embodiment of the invention, each of the electrical
resistance heaters 34 and 36 is of the self-regulating type formed
of a ceramic material or the like which has a positive temperature
coefficient of resistivity (PTC) and which is adapted to display a
sharp, anomolous increase in resistivity when self-heated to a
selected temperature for limiting further increase in the
temperature of the heater. Typically for example, the heaters each
comprise a disc element of a lanthanum-doped barium titanate or the
like having a diameter of 0.300 to 0.800 inches and a thickness of
about 0.050 inches and having metal contact layers (not shown) on
opposite surfaces 34.1-34.2 and 26.1-36.2 of the elements to make
ohmic contact to the ceramic material and to serve as terminals of
the heater elements. As such PTC heaters are well known, they are
not further described and it will be understood that each heater
displays only 1-3 ohms resistance when electrical current is
directed through the element at room temperature but displays about
20-30 ohms resistance when self-heated to a temperature of about
120.degree. C. or the like at which the heater temperature
stabilizes.
In the preferred embodiment of the invention, the first heat-sink
plate 38 is very thin and the fixed end of the spiral thermostatic
coil spring 20 is secured at one side 38.1 of the plate by the stud
20.1 so that the coil convolutions lie along said one side of the
plate. The second heater 36 is mounted at the opposite side 38.2 of
the plate at a central location on the plate. Typically, the stud
20.1 which secures the spring to the plate also mounts the heater
element 36 on the back of the stud as illustrated in FIG. 2.
Preferably the ohmic contact layer on one side 36.1 of the second
heater element is electrically connected to the plate 38 by a
conductive adhesive or solder or the like (not shown) and
preferably the thin plate has spacer bumps 38.3 distributed around
the perimeter of the plate side 38.2.
The second heat sink plate 40 is relatively much thicker than the
plate 38 and has a central recess or opening 40.1 in the plate. One
side 40.2 of the plate is disposed in heat transfer relation to
said opposite side 38.2 of the thin heat sink plate, preferably by
being abutted against the spacers 38.3, and the central recess or
opening 30.1 is fitted around the second heater 36 as is shown in
FIG. 2. A tang or platform part 40.3 of the plate extends over the
recess or opening 40.1 from the opposite side 40.4 of the plate and
the first heater element 34 is preferably mounted on that tang or
platform-part of the plate. Preferably the ohmic contact layer
formed on one side 34.1 of the first heater is electrically
connected to the plate 40 by a conductive adhesive or solder or the
like (not shown).
In a preferred embodiment of the invention, an electrical insulator
42 of a relatively stiff organic material has a groove 42.1
receiving an edge of the tang or platform part 40.3 of the thicker
heat sink plate and has wings 42.2 press-fitted into the opening
40.1 in the plate for securing the insulator in the plate opening
40.1. A spring conductor or jumper 44 has a bight portion 44.1
gripping the insulator and has one end 44.2 electrically engaged
with the ohmic contact surface on the opposite side 36.2 of the
second heater element whereby the conductor extends through the
opening 40.1 in electrically insulated relation to the plate 40 to
dispose the opposite end 44.3 of the conductor to be accessible at
the side 40.4 of the plate. The plates 38 and 40 are formed of
materials of high thermal conductivity such as aluminum or copper
or lower thermal conductivity such as low carbon or stainless steel
materials as may be desired.
In a preferred embodiment of this invention, a gasket ring 46 of
thermally insulating material is disposed between selected portions
of the heat-sink plates 38 and 40 as shown in FIG. 2 for
restricting heat-transfer between those plates to a desired extent.
Rivets 48 or the like then secure the housing 22, the heat sink
plate 40, and the heat sink plate 38 together in any conventional
manner so that the gasket 46 is secured between the two heat sink
plates, so that O-ring gaskets 50 are clamped between the housing
and the plate 40 and between the housing and terminal 30 and so
that the heat-sink plates are electrically connected together in
selected heat-transfer relation to each other and to the
thermostatic spring 20. The first heater 34 is spaced from the
spring 20 by a heat-transfer path of substantial effective length
extending across the platform part 40.3 of the plate 40, through
the plate 40, through the restricted spacer bumps 38.3 and the
plate 38 to the spring 20. The second heater 36 is spaced from the
spring 20 by a much shorter heat-transfer path extending through
the stud 20.1 or the thin plate 38. The gaskets 46 and 50 seal the
heater elements 34 and 36 within the control 10 to protect the
elements from the surrounding atmosphere. The attachment of the
housing 22 to the heat sink plates also holds the spring terminal
26 in electrical engagment with the end 44.3 of the conductor 44
and holds the spring terminal 28 in electrical engagement with the
ohmic contact layer on the side 34.2 of the first heater
element.
In accordance with this invention, strap means 52 are attached by
screws 52.1 to the choke mounting housing 12.1 on the carburetor
and extend over portions of the housing 22 for adjustably mounting
the choke control 10 on the carburetor in conventional manner so
that the tang 20.2 on the thermostatic spring engages the bell
crank 18.1 of the choke valve linkage and so that the heat sink
plates 38 and 40 are connected to electrical ground through the
housing 12.1 in conventional manner. Preferably as is indicated
only in FIG. 2 by the broken lines 54, a sleeve of polyurethane
foam or other thermal insulating material is preferably disposed
over the choke control 10, and preferably over part of the choke
mounting housing 12.1, for surrounding the heaters 34 and 36, the
heat sink plates 38 and 40, the spring 20 and the thermally
responsive switch 24.
In that arrangement, when the engine 14 is started on a cold day,
the thermostatic spring 20 urges the choke valve 18 to its closed
position so that a fuel-enriched air-fuel mixture is furnished to
the engine and so that the engine runs smoothly even though the
air-fuel intake portions 14.1 and the like of the engine are not at
the temperature at which they assure full vaporization of the fuel
being furnished to the engine. The terminal 30 of the choke control
10 is connected to an electrical power source indicated by the lead
56 in FIG. 2 on closing of the engine ignition switch or the like
when the engine is started. Accordingly electrical current is
directed through rivet 28.1, terminals 28, heater 34, plates 40 and
38 and through the mounting housing 12.1 to electrical ground for
energizing the heater 34 as soon as motor operation is initiated.
Since the ambient temperature is low, the thermally responsive
switch 24 is not actuated and the second heater 36 is not
energized. In that situation, heat generated by heater 34 is
transferred to the plate 40 and tends to spread out through the
plate to be gradually transferred into and through the plate 38 to
the thermostatic spring 20. Since the heat-transfer path between
the first heater and the spring is of substantial effective length,
the actual transfer of heat into the spring 20 occurs only with a
selected delay after the initiation of engine operation.
Accordingly the spring 20 continues to apply its initial
choke-valve-closing force to the valve 18 during that delay and the
choke system continues to furnish the initial degree of fuel
enrichment for assuring smooth engine operation even if the engine
should be sharply accelerated shortly after engine start-up.
Thereafter, heat continues to be transferred to the spring 20 so
that the choke valve is subsequently permitted to open to eliminate
such fuel enrichment when the noted air-fuel intake portions of the
engine have been heated to their desired fuel vaporizing
temperature.
Alternately, if the engine is started when ambient temperature is
above the actuating temperature of the thermally responsive switch
24, that switch is closed when engine operation is initiated.
Electrical current is therefore directed through terminal 30,
spring 24.2, snap-disc 24.1, rivet 26.1, terminal 26, conductor 44,
heater 36, plate 38 and through mounting housing 12.1 to electrical
ground for energizing heater 36 as soon as the engine is started.
In that situation, heat is transferred from the heater 36 through
plate 38 to the spring 20. Since that heat-transfer path between
the second heater and the spring is relatively short, the actual
transfer of heat into the spring 20 occurs promptly after the
initiation of engine operation and reduction of the
choke-valve-closing force of the spring promptly begins. The
heaters 34 and 36 then cooperate is heating the spring so that the
enrichment of the fuel being furnished to the engine is quickly
eliminated. In a preferred embodiment of this invention,
heat-transfer means in the choke control 10 also define a third
heat-transfer path between the first heater 34 and the thermally
responsive switch 24, whereby, when the engine 14 is started on a
cold day while the switch 24 is unactuated, heat from the heater 34
is conducted to the switch for actuating the switch after a desired
period of time to energize the second heater 36. Preferably the
control 10 is proportioned so that heat from the heater 34 is
transferred through the rivets 26.1 and 28.1 and the like so that
the switch 24 is actuated after the actual transfer of heat from
the first heater 34 to the spring 20 has begun and before heat from
the heater 34 has heated the spring to its full choke opening
temperature. In that way, the second heater 36 is adapted to
cooperate with the first heater in completing opening of the choke
once the choke adjustment period has begun.
In accordance with this invention, the heat-transfer means in the
choke control 10 are provided with sufficient heat storage capacity
to continue to transfer heat to the spring 20 for a substantial
period of time after operation of the engine 14 is terminated,
whereby, for at least a major part of the delay period before the
noted air-fuel intake portions 14.1 and the like of the engine cool
below their noted fuel vaporizing temperature, the spring 20 is
maintained at a temperature which prevents any substantial fuel
enrichment if the engine should be restarted during that cool down
period. In that way the choke contol 10 tends to avoid fuel waste,
to avoid excessive emission of exhaust pollutants, and avoid
possible flooding of the engine during such restarting.
Typically for example, the plates 38 and 40 have thicknesses of
0.025 and 0.200 inches respectively and each have a diameter of
about 2.0 inches. Thus, in providing the desired different
heat-transfer paths between the heaters 34 and 36 and the spring
20, the plates also provide the control 10 with substantial
heat-storage capacity. Therefore particularly when the thermal
insulating gasket is disposed between the plates 38 and 40 for
restricting heat transfer from the plate 40 to the plate 38 it is
found that the heat sink plates continue to transfer heat to the
spring 20 to maintain that spring at a choke opening temperature
for a major part of the time during which the air-fuel intake
protions 14.1 and the like of the engine remain above their desired
fuel vaporizing temperature. Further, if the control 10 is enclosed
in the thermal insulating sleeve 54 for retaining heat within the
control after the termination of engine operation, the heat-sink
means maintain the spring 20 at that choke opening temperature for
substantially the entire cool down period of the engine.
In a typical embodiment of the invention, where the heater 34 in
the choke control 10 is energized at 0.degree. F., the tang 20.2 of
the thermostatic spring is initially disposed at an angle of
-60.degree. relative to a selected reference point as indicated by
curve 58 in FIG. 4 and, for a brief period after the heater 34 is
energized, the spring tang substantially retains its initial
position as heat is being transferred through the heat sink plates
38 and 40. Even by the end of about four minutes after energization
of the heater 34, the coil tang 20.2 has moved through an angle
less than about 40.degree.. However, in that period, heat from the
heater 34 heats the thermally responsive switch 24 to its actuation
temperature for energizing the second heater 36, whereby the two
heaters thereafter cooperate in heating the coil to move the coil
tang through an additional angle of more than 65.degree. in about
two additional minutes. The choke control 10 is thus adapted to
provide an initial delay in reducing the choke valve closing force
of the spring 20 after energization of the heater 34 on a cold day
to assure smooth engine operation but is thereafter adapted to
reduce the spring force rapidly to eliminate fuel enrichment by the
choke valve in about six minutes in an ambient temperature of about
0.degree. F.
Then, subsequently, when the heaters 34 and 36 are deenergized in
the ambient temperature of 0.degree. F. while the spring 20 and the
heat-sink plates 38 and 40 are fully heated so that the coil tang
20.2 is disposed at an angle of about +60.degree. as is indicated
by curve 60 in FIG. 5, the heat sink plates store sufficient heat
to continue to transfer heat to the spring 20 for a substantial
period of time after the heaters are deenergized. Thus, even where
the thermally insulating sleeve 56 is omitted from the control 10,
the heat-transferred to the spring retains the coil tang at an
angle of -15.degree. for about 10 minutes as indicated by curve 60.
Thus, the choke control 10 is adapted to maintain the spring 20
with a substantially reduced choke valve closing force for at least
a major part of the time before the air-fuel intake portions of an
engine using the choke control would cool below their fuel
vaporizing temperatures. Further, where the thermal insulating
sleeve 54 is used around the choke control, the control is adapted
to retain the spring 20 with a substantially reduced choke valve
closing force for substantially the entire cool down period of the
engine.
The choke control 10 is also characterized by its modular
construction as described above wherein the ratings of the heaters
34 and 36 and the proportions of the heat sink plates 38 and 40 are
relatively variable for matching the warm-up and cool down
characteristics of various engines while still being economically
combined with the housing 22.
It should be understood that although particular embodiments of
this invention have been described by way of illustrating this
invention, the invention includes all modifications and equivalents
of the described embodiments falling within the scope of the
appended claims.
* * * * *